REFURBISHMENT

Creating a Grease-Free Environment At

By William O. Moss open in about five seconds and close in 20 seconds. Pump-turbine units The 1,728-MW Dinorwig Pumped-Storage Power Station in are kept spinning-in-air, synchro- the undergoes many modes changes per day nized to the grid, ready to provide a in providing system stability and reserve for the national grid rapid reserve of electricity in the in England and . In doing so, its greased bronze turbine event of a plant failure or sudden bearings sustain severe wear. After conducting extensive tests, peaks in demand. This standby operator First Hydro decided to install grease-free bearings, mode gives Dinorwig the fastest response time of any pumped-stor- with the help of an innovative in-situ milling machine. age power station in the world. In approximately 12 seconds, the out- put of Dinorwig can be ramped n original specification Playing a special role from zero to 1,320 MW. for the six-unit, 1,728- Dinorwig’s role in protecting the The site chosen for the power MW Dinorwig Pumped- national grid for England and Wales station was the Dinorwig Storage Power Station was adopted during the 1970s when quarry that operated for more than inA called for the facil- the Central Electricity Generating 160 years, up until World War II. ity to be capable of 40 mode Board, then the primary electric The station was built in a man- changes per day for at least a full sector regulatory agency, selected made cavern inside the mountain, 12-month period without any sche- the concept of hydroelectric pumped Elidir Mawr, on the boundary of duled maintenance. Since its com- storage as the best option for fre- the National Park. missioning in 1982, Dinorwig has quency regulation and reserve. Each of the six reversible Francis- fulfilled the requirement. Overall electricity demand was type pump-turbine units can pro- However, owing to the particu- rapidly increasing. The trend in- duce up to 288 MW of electricity at larly onerous operating condi- volved construction of 500- to 660- 18 KV, producing a total of 1,728 tions, some of the grease-lubri- MW baseload thermal units, with MW. On-site transformers step up cated bronze turbine bearings the possibility of building thermal the voltage to 400 KV. The electric- have sustained severe wear and units twice that size. The concern ity leaves the site through under- have had to be replaced as often was that if one or two units failed, ground cables and connects to the as every two years. This, together the grid would have to be reinforced national grid at a substation in with the operational and mainte- within 10 to 15 seconds or the power Pentir 9.7 kilometers away. nance costs and adverse en- system would collapse. That is where Alternatives to vironmental effects of frequent the Dinorwig Pumped-Storage Sta- greased bearings pumping of grease, led to a review tion comes into the picture. of grease-free alternatives for Dinorwig features fast-opening As a result of providing rapid fre- these bearings. spherical valves that permit early quency stabilization and reserve opening of the guide vanes during power, Dinorwig’s grease-lubricated starting or loading from a “spin- bronze turbine bearings sustain Bill Moss is mechanical engineering manager for First Hydro Company, ning-in-air” condition. Dinorwig’s continual wear. In the mid-1990s, which manages and operates the six main rotary inlet valves — one First Hydro decided to explore Dinorwig Pumped-Storage Power for each unit — are among the using grease-free bearings. Station in the United Kingdom. fastest in the world, designed to In exploring the greaseless bear-

From HRW, November 2001 - © HCI Publications, www.hcipub.com Reproduced with permission ings available on the market, First the use of materials for specific Hydro mechanical engineer, de- Hydro engineers discovered that applications. signed a new bearing arrange- none of the existing tests of avail- Orkot TXM bearings were cho- ment. This design incorporated a able materials was applicable to sen to replace the original grease- stainless steel liner to be attached Dinorwig because of the plant’s lubricated bronze guide vane upper to the existing worn track. The unusually demanding operating and intermediate bearings and the regulating ring bearing is “L- conditions — conditions that would regulating ring servomotor connect- shaped,” and so has a horizontal have been difficult to recreate in ing rod link bushings. Lubron AQ30 and a vertical part. It has a rota- the laboratory. As a result, First bearings were chosen to replace the tional movement of only 34 de- Hydro engineers decided to test original guide vane bottom bearing, grees at a relatively slow speed. bearing materials in-situ, in order the regulating ring servomotor con- The pressure-velocity value for the to achieve accurate and directly necting rod spherical bearing, and bearing was calculated, yielding useful results. the regulating ring bearing. the conclusion that a full 360- Guide vane bearings were cho- degree bearing was not required. Focus on replacement of the sen for the tests. The upper bearing Instead, a segmented bearing de- regulating ring bearing of this assembly is exposed to the sign would be adequate. most severe conditions and shows In replacing the regulating ring The bearing itself is made up of the worst wear rates of all the bearing, First Hydro engineers 24 segments (12 horizontal and 12 grease-lubricated bearings on the discovered a difficult and poten- vertical). The stainless steel liner is turbines. There are 72 such bear- tially expensive problem. The new in 20 segments (12 horizontal and ings (24 upper, 24 intermediate, bear-ing that was selected is an eight vertical). The segments of the and 24 bottom) on each of the six aluminum bronze bearing with bearing and liner are carefully posi- turbines. They, therefore, offered AQ30 PTFE (polytetrafluoroethyl- tioned so that the bearing segments many prospective locations for test- ene) solid lubricant inserts. To do move off of the stainless steel ing a large number of the available ensure a long life for a self-lubri- liners on rotation. greaseless bearings. cating bearing, the counter-face In order to accommodate the In 1996, First Hydro offered must have adequate hardness, a thickness of the stainless steel lin- several greaseless bearing manu- good surface finish, and no corro- ers and to repair the damage found facturers the opportunity to par- sive products. Consequently, the on the existing track, the top cover ticipate in the tests by supplying existing carbon steel track, which vertical and horizontal bearing their self-lubricating bearings for was scratched and corroded, was track required machining. Nor- the guide vane application. Each not suitable. mally, machining this track would manufacturer supplied two identi- Burgess Hatem, a Senior First require stripping down the unit, cal bearings for each position, sized to fit the existing housings. The tolerances and clearances were agreed upon between First Hydro and engineers from each of the manufacturers. To monitor wear rates, proximity probes were mounted on one bear- ing from each pair. Each pair was separated in order to find out if there was any position effect. The bearings were removed and in- spected as opportunities permitted, and, if performing well, were rein- stalled for continued testing. A total of three years was spent on the testing program. The effort included researching, testing, mon- itoring, and developing alternative This photograph shows a new self-lubricating Lubron AQ30 regulating ring materials. Then, in 1999, First bearing in place at the in the United Kingdom, the last Hydro made decisions regarding step in First Hydro Company’s goal to create a completely grease-free turbine.

HRW / November 2001 2 Existing tracks for regulating ring bearings at the 1,728- ment self-lubricating bearings, plant operator First Hydro MW Dinorwig Pumped-Storage Power Station in the United Company designed a stainless steel liner to be attached to Kingdom were scratched and corroded, as shown in the the track, as shown in the photograph on the right, that photograph on the left. To ensure a long life for replace- provided a hard, smooth surface with no corrosive activity. which would result in weeks of Kingdom, a specialist in on-site feasibility of further adapting the downtime and lost generation. This machining. device to machine the top cover. would require that the regulating Extensive development work fol- Innovations in ring bearing be split and removed. lowed. First Hydro supplied the re- on-site machining Then, the 5.5-meter-diameter, 100- quirements, while Furmanite adap- ton top cover would need to be First Hydro’s previous experience ted the machine to the application. removed and taken to a workshop with Furmanite included a similar The main adaptation was to assem- for machining. The cost due to man- in-situ machining problem on the ble and rotate the machine around power and loss of productivity bottom cover at Dinorwig. To carry the turbine’s main shaft. For this, a would be huge. out that work, Furmanite had special split-bearing sleeve was If this machining could be adapted a device it already had designed, along with a clocking arm done without removing the top designed — the Circular Self- for setting the sleeve up concentri- cover, downtime and manpower Leveling Milling Machine. The cally with the bearing track. Of could be dramatically reduced. In machine makes use of a sophisti- major importance was the flatness the search for such an in-situ cated control system that adjusts of the bearing track, but this was machining device, First Hydro the machining plane to follow a pre- easily achieved with the milling ma- Company approached Furmanite determined reference plane. First chine’s self-leveling technology and International Ltd of the United Hydro asked Furmanite about the a specially designed split datum ring. The datum ring was pre-set using Furmanite’s precision scan- ning laser system to give very high accuracy. In order to minimize the risk of problems once on-site at Dinor- wig, the adapted machine was tested and final adjustments were made on a full-sized mock-up of the shaft and bearing track at Furmanite’s workshop. Furmanite demonstrated the machine for First Hydro engineers, then sub- mitted a full risk assessment and method statement to First Hydro for review before arriving on-site. Grease-free at last! A split-bearing sleeve, shown above, was designed by First Hydro Company and contractor Furmanite to help guide a milling machine as it rotated around In 1999, the grease-lubricated the main turbine shafts during a bearing replacement project at the 1,728-MW bronze bearing on Unit 6 was re- Dinorwig Pumped-Storage Power Station. placed by the Lubron AQ30 self-

HRW / November 2001 3 lubricating segmented bearing. commissioning the unit, numerous and saved on the cost of grease and Furmanite machined the bearing checks were made on the regulating grease dispensing equipment. track (horizontal and vertical) ring bearing. All was well. The new In the long term, the self-lubricat- using the specially developed bearing segments ran smoothly on ing bearings will provide First milling machine, removing approxi- the new stainless steel liners. Hydro with very substantial cost mately 3 millimeters of material savings owing to the extended ser- The future is bright! before fitting the stainless steel vice life, which is at least three times liner segments. Now, in 2001, five of the pump- that of the original grease-lubricated This was the last step to a turbine units at Dinorwig have bearings, thus extending the time grease-free turbine. The work was undergone the bearing replace- between routine maintenance and successfully completed and the ment procedure and are totally reducing the annual expenditure on process — including set-up, ma- grease-free. Work on the sixth and replacement bearings. L chining, bearing and liner seg- final unit is scheduled for 2002. ment fitting, and de-rigging — The move toward grease-free Mr. Moss may be contacted at First Hydro Company, Dinorwig Pumped- took only nine days, with crews units has aided First Hydro in its Storage Power Station, , working 24 hours a day. pursuit and retainment of ISO , North Wales LL55 4TY The vertical bearing track dia- 14001 certification (International United Kingdom; (44) 1286-873213; meter was measured using a pre- Standard for Environmental Man- Fax: (44) 1286-873252; E-mail: cision circumference tape. The agement) for the Dinorwig Power [email protected]. flatness of the horizontal track was Station. The absence of grease also Reference: measured using the precision scan- has greatly improved the immediate ning laser system, and found to be working environment around each Moss, W.O, and B. Hatem, “Testing within an acceptable 0.15 millime- generating unit, eliminated the risk Greaseless Bearings in Service,” ter of the flatness required. On re- of grease ingress into the lake water, HRW, March 2000, pages 8-10.

HRW / November 2001 4